Zinc(ii) mediated synthesis of an N-substituted 2-(2-pyridyl)imidazole from a 1,2-diketone and 2-(aminomethyl)pyridine and its ligational behaviour

Abstract

Reaction of anhydrous ZnCl2 with the 1∶2 condensate (L) of benzil and 2-(aminomethyl)pyridine in methanol gives monomeric ZnL′Cl2 (1) where L′ is 2-[(4,5-diphenyl-2-pyridin-2-yl-1H-imidazol-1-yl)methyl]pyridine. In the X-ray crystal structure, 1 is found to contain tetrahedral zinc with an N2Cl2 coordination sphere and the N-substituent methylpyridine fragment hanging as a free arm. A tentative mechanism is proposed for the zinc mediated conversion of L→L′. Demetallation of 1 by the action of aqueous NaOH yields L′ in the free state. When L′ is reacted with Zn(ClO4)2·6H2O in a 1∶2 molar proportion, [Zn(L′)2]n(ClO4)2n·(H2O)n/2·(CH2Cl2)n/2 (2) is obtained. The zinc atom in 2, as revealed by X-ray crystallography, has a trigonal bipyramidal N5 coordination sphere. There are two independent ligands in the asymmetric unit of 2. One of them bonds only to one zinc atom in a bidentate mode with the N-substituent methylpyridine hanging free while the other ligand binds to two different zinc atoms in a tridentate fashion, employing the N-substituent methylpyridine nitrogen atom to form the polymeric one-dimensional chain cation.